1. Field of the Invention
The present invention relates to an image processing device, an image processing method and an image processing program for aligning and displaying a three-dimensional moving image taken with a CT or MR apparatus with a two-dimensional or three-dimensional moving image taken with an ultrasonic diagnostics apparatus.
2. Description of the Related Art
In the medical field, detailed three-dimensional moving images, which are obtained by imaging a body part of a patient making a predetermined periodic motion, such as the heart, with a modality having high spatial resolution and contrast resolution, such as a CT or MR apparatus, are widely used for imaging diagnosis.
On the other hand, ultrasonic moving images taken with an ultrasonic diagnostics apparatus, which has no problem of radiation exposure, etc., allows examination with a simple device, and provides information about blood flow based on reflection of ultrasonic waves by the blood flow, are also effective for imaging diagnosis. Further, along with the development of the ultrasound diagnostic technique, three-dimensional ultrasonic moving images of subjects have become available as the ultrasonic moving images, in addition to conventional ultrasonic moving images obtained with respect to a predetermined two-dimensional cross section of subjects.
In order to use advantages of both the above-described moving images, doctors conduct the imaging diagnosis with displaying both the moving images in a state where they show the same phase of heart beat based on electrocardiographic data that is obtained during imaging of each moving image. At this time, the user (doctor) references one of the images with manually changing the position and direction shown in the other of the images to be the same as those shown in the one of the images so that the moving images showing the same position and phase are displayed at the same time on a display in a manner allowing comparison therebetween. However, while a CT or MR image is taken in fixed position and orientation relative to the subject, an ultrasonic image is taken with pressing an ultrasound probe against the subject at an arbitrary angle. Therefore, it is difficult to identify the position and direction of the ultrasonic image relative to the subject. Further, it is necessary to identify a frame image forming the CT or MRI moving image and a frame image forming the ultrasonic moving image that correspond to the same phase. Therefore, it imposes significant time and labor on the user to display these moving images in a manner allowing comparison therebetween.
Japanese Unexamined Patent Publication No. 2003-153877 (hereinafter, Patent Document 1) has proposed a technique which involves: extracting a predetermined characteristic part, such as a blood vessel area including a blood flow image, from ultrasonic image data of an examined body part; aligning the position of the predetermined characteristic part shown in the ultrasonic image with the position of the predetermined characteristic part shown in an MR image obtained in advance; correcting the MR image such that the MR image and the ultrasonic image show the predetermined characteristic part in the same position; and superimposing the corrected MR image and the ultrasonic image and displaying the superimposed image on a display device.
Further, Japanese Unexamined Patent Publication No. 2009-022459 (hereinafter, Patent Document 2) has proposed a technique which involves: synchronizing timing of a three-dimensional CT moving image with timing of a three-dimensional ultrasonic moving image based on electrocardiographic data; reconstructing the ultrasonic image by transforming a spatial coordinate system of the ultrasonic moving image into a spatial coordinate system of the CT moving image using a transformation matrix; and displaying the reconstructed moving images being aligned and superimposed.
According to the technique taught in Patent Document 1, it is able to spatially align a three-dimensional still image taken with a CT apparatus with an ultrasonic still image. However, with the technique taught in Patent Document 1, a three-dimensional moving image taken with a CT apparatus and an ultrasonic moving image cannot be associated with the phases of heart beat, and therefore it is difficult to display the moving images such that they show the same phase and the same spatial position to allow comparison therebetween. Further, according to the technique taught in Patent Document 2, it is necessary to obtain electrocardiographic data corresponding to the moving images to align the moving images with each other with respect to the phase of heart beat. Therefore, in a case where the electrocardiographic data corresponding to one of or both of the moving images is not available, it is difficult to associate the corresponding phases of heart beat shown in the moving images with each other.